Heavy Barbell Curls will do the trick. Stick to 5x5 for a few weeks and see what happens. Vary your grip and use a straight bar one week and a curl bar the next. A narrow grip will get the outsides of your bis and a wide grip the insides.

Biceps are a lagging part for me as well so I hit them twice a week. Once with a Back/hamstring day and then again at the end of the week for an arm day. I've noticed great size improvements with this.